1. Field of the Invention
The present invention relates to a circuit for correcting a horizontal deflection, and more particularly to a horizontal-deflection correction circuit providing either or both a S-shaped correction and a linear correction of a sawtooth current flowing in a horizontal deflection coil.
2. Background Art
In general, a cathode ray tube (CRT) employed in a video display apparatus uses a principle displaying different brightness and colors by striking fluorescent materials of red (R), green (G), and blue (B) coated on a surface of the cathode ray tube with a different amount of an electronic beam according to an intensity of a video signal, and is widely used since its price and its display performance are widely accepted. The video display apparatus receives a video signal and a synchronization signal from a video card of a personal computer and display images on the screen of the cathode ray tube. Rasters may be formed on the entire screen of the cathode ray tube by deflecting an electronic beam irradiated from the electron gun to the horizontal and vertical directions by supplying sawtooth currents to the horizontal deflection coil and the vertical deflection coil. Accordingly, if the microcomputer outputs a plurality of additional control signals with a low level or a high level corresponding to the horizontal frequency, transistor switches are respectively turned on or off, so auxiliary correction capacitors connected to the deflection coil are selectively either incorporated into the circuit or are switched out of the circuit and the magnitude of the sawtooth current is varied. The edge portions of the screen grow wider than the center portion however, because of the change from the horizontal frequency from a low frequency to a high frequency. Inductances of coils vary according to the magnitude and direction of current flow, so that the magnitude and the direction of the sawtooth current flowing through the horizontal deflection coil vary. In a horizontal-deflection correction circuit constructed according to contemporary design practice, since an entire capacitance is determined by switching plural capacitors by plural S-shaped correction control signals and an average capacitance is allocated by dividing a horizontal synchronization signal into several frequency bandwidths, I have noticed that an exact S-shaped correction is not obtained in correspondence with the respective horizontal frequencies, but that only an approximate S-shaped correction is achieved. In order to control the circuit of the present invention by plural S-shaped correction control signals, since a microcomputer equipped with plural S-shaped correction control ports is required and plural S-shaped correction capacitors and plural switching devices are required; production costs are increased however, and I have found that the correction circuit is complex in structure and its implementation is difficult and requires too much space for installation on a printed circuit board built into a monitor.
It is an object of the present invention to provide an improved horizontal-deflection process and circuit.
It is another object to provide a simplified horizontal-deflection correction process and circuit that may implemented with a lower per unit cost, with a lower rejection rate.
It is yet another object to provide a horizontal-deflection correction process and circuit that may be constructed with fewer capacitors.
It is still another object to provide a horizontal-deflection correction process and circuit that requires fewer switching stages.
It is still yet another object to provide a horizontal-deflection correction process and circuit amenable to miniaturization and compact circuit board construction.
It is a further object to provide a horizontal-deflection correction process and circuit capable of making an S-shaped correction and a linearity correction with respect to a sawtooth current flowing in a horizontal deflection coil by supplying correction currents to double variable coils having opposite polarity to each other according to a horizontal frequency.
These and other objects may be attained with a horizontal-deflection correction circuit providing either or both a S-shaped correction and a linearity correction on the basis of a sawtooth current flowing in a horizontal deflection coil by supplying correction currents to double variable coils having opposite polarity to each other according to a horizontal frequency. A horizontal-deflection correction circuit may be constructed according to the principles of the present invention with a horizontal deflection stage for deflecting a scan electronic beam in a horizontal direction by a sawtooth current flowing in horizontal deflection coil; a control stage outputting a first and second control voltages which have the same value in case of performing a linear correction and outputting the first and second control voltages which have different values in case of performing a S-shaped correction; a first correction stage for varying an inductance of a first variable inductor connected in series to the horizontal deflection coil according to the first control voltage and correcting a magnitude and a direction of the sawtooth current; and a second correction stage for varying an inductance of the second variable inductor connected in series to the first variable inductor in an opposite polarity and correcting the magnitude and the direction of the sawtooth current.
In the practice of the principles of the present invention, the horizontal-deflection correction circuit supplies correction currents to double variable coils having opposite polarities to each other, respectively, according to horizontal frequencies to perform at least one or more S-shaped correction or linearity correction with respect to a sawtooth current flowing in the horizontal deflection coils, so that the number of capacitors for the S-shaped correction and the number of switching stages are greatly reduced to lower the production cost as well as to simplify a circuit construction for an easy embodiment so that a market-rejection rate is remarkably reduced, compared to a contemplated horizontal-deflection correction circuit. When the horizontal-deflection correction circuit performs an approximate S-shaped correction according to respective horizontal frequencies by allotting an average capacitance by dividing a horizontal synchronization signal by frequency bandwidths, the horizontal-deflection correction circuit according to an embodiment of the present invention determines variable inductances according to respective frequencies of a horizontal synchronization signal to perform an exact S-shaped correction.